1. Field of the Invention
The present invention relates to a substrate treatment method and a substrate treatment apparatus. Exemplary substrates to be treated include semiconductor wafers, substrates for liquid crystal display devices, substrates for plasma display devices, substrates for FED (Field Emission Display) devices, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, substrates for photo masks, ceramic substrates and substrates for solar cells.
2. Description of Related Art
In production processes for semiconductor devices, liquid crystal display devices and the like, a single substrate processing type substrate treatment apparatus which is adapted to treat a single substrate at a time is often used. The conventional substrate treatment apparatus of the single substrate processing type includes a spin chuck which horizontally holds and rotates the substrate, and a nozzle which spouts a treatment liquid to a front surface of the substrate rotated by the spin chuck.
In a substrate treatment process using the substrate treatment apparatus, a chemical liquid treatment process and a rinsing process are performed in this order, for example, by sequentially supplying a chemical liquid and pure water to the front surface of the rotating substrate. Thereafter, an isopropyl alcohol (IPA) liquid is supplied to the front surface of the substrate. After the supply of the IPA liquid, the substrate is kept in a puddle state with the entire front surface thereof covered with a liquid film of the IPA liquid, while being kept in a non-rotation state or in a lower speed rotation state. Then, the substrate in the puddle state is accelerated in its rotation direction, whereby a spin drying process is performed to spin off the IPA liquid present on the substrate.
JP2009-212408A1, for example, proposes a prior-art method in which a liquid film of pure water is formed as covering the entire front surface of the substrate before the formation of the IPA liquid film after the rinsing process in the aforementioned process sequence.
In this prior art method, the pure water is spouted from a nozzle after the rinsing process. At the same time, the substrate is decelerated from a rinsing rotation speed to zero or a lower rotation speed. Therefore, a centrifugal force acting on the pure water present on the substrate is reduced to zero or a lower level. As a result, the pure water present on the front surface of the substrate is stagnated, so that the pure water liquid film is retained on the substrate as covering the entire front surface of the substrate. In turn, the pure water liquid film is replaced with the IPA liquid, whereby a liquid film of the IPA liquid is formed on the substrate as covering the entire front surface of the substrate. At this time, the pure water present on the substrate is partially dissolved in the IPA liquid to form a portion of the IPA liquid film. Therefore, the consumption of the IPA liquid can be saved.
However, it is sometimes difficult to cover the entire front surface of the substrate with the pure water liquid film depending on the surface characteristics and the size of the substrate. Where the front surface of the substrate is hydrophobic, for example, the pure water has a greater contact angle with respect to the front surface of the substrate and is likely to be repelled on the front surface of the substrate. Therefore, the front surface of the substrate is likely to have a portion uncovered with the pure water. Particularly, the portion uncovered with the pure water is likely to be present on a peripheral edge portion of the substrate. In the case of a large-scale substrate (e.g., around substrate having an outer diameter of 450 mm), this tendency is remarkable.
For establishment of the puddle state, the rotation speed of the substrate is reduced from the higher speed to the lower speed. Where the highly hydrophobic substrate or the large-scale substrate described above is used, however, quick deceleration of the substrate is likely to split the liquid film present on the front surface of the substrate to expose a portion of the front surface of the substrate. Where the rotation speed of the substrate is slowly reduced, a longer time is required to establish the puddle state. As the time required for the establishment of the puddle state increases, the entire process time is increased, thereby reducing the throughput of the substrate treatment apparatus (the number of substrates treated per unit time).